Three-dimensional models of elasto-static deformation in heterogeneous media, with applications to the Eastern California Shear Zone

Sylvain D. Barbot, Yuri Fialko, & David T. Sandwell

Published 2009, SCEC Contribution #1266

We present a semi-analytic iterative procedure for evaluating
three-dimensional (3-D) deformation due to faults in an arbitrary
heterogeneous half space. Spatially variable elastic properties are
modeled with equivalent body forces and equivalent surface tractions
in a homogeneous elastic medium. Displacement field is obtained in the
Fourier domain using semi-analytic Greens' functions. We apply this
model to investigate the response of 3-D compliant zones (CZ) around
major crustal faults to coseismic stressing by nearby earthquakes. We
constrain the two elastic moduli, as well as the geometry of the fault
zones by comparing model predictions to the data. Our results confirm
that the compliant zone models for the Rodman, Calico and Pinto
Mountain faults in the Eastern California Shear Zone can explain
coseismic InSAR data from both the Landers and the Hector Mine
earthquakes. For the Pinto Mountain fault zone, InSAR data suggest a
60% reduction in effective shear modulus and a 7% increase in
Poisson's ratio compared to ambient crust. Large wavelength of
coseismic LOS displacements around the Pinto Mountain fault require a
fairly wide (1.5 km) CZ extending to depth of at least 9 km. Best fit
for the Rodman and the Calico CZs, north of Galway Dry Lake, is
obtained for a 4.5 km deep compliant zones, with a 60% reduction in
shear modulus for both fault zones, and 20% increase in Poisson's
ratio for the Rodman fault CZ, and no change in Poisson's ratio for
the Calico fault CZ. We find that the required effective rigidity of
the Calico fault zone south of Galway Dry Lake is not as low as that
of the northern segment, suggesting along-strike variations of
effective elastic moduli within the same fault zone. The inferred
width of compliant fault zones in the Mojave desert varies between 0.8
and 1.5 km. These observations suggest pervasive and widespread
damage around active crustal faults.

Citation
Barbot, S. D., Fialko, Y., & Sandwell, D. T. (2009). Three-dimensional models of elasto-static deformation in heterogeneous media, with applications to the Eastern California Shear Zone. Geophysical Journal International, 179, 500-520. doi: 10.1111/j.1365-246X.2009.04194.x.